The invention relates generally to the manufacture of integrated circuits and the like; and, more specifically, to the recycling/reclamation of monitor or test wafers used for testing and evaluating steps in the processing of semiconductor wafers used in such manufacturing.
In the manufacture of integrated circuits and the like, hundreds of individual manufacturing steps are required to convert a bare silicon wafer into one or more operational integrated circuits (ICs). In an effort to save time and money, after an individual manufacturing step is set up, a monitor or test wafer (“monitor wafer”) is processed through the given manufacturing step to determine whether the manufacturing step achieves its intended purpose. If the specific manufacturing step being tested achieves its intended purpose, then the manufacturer is confident that actual device wafers (viz., production wafers) may be subjected to the manufacturing step. However, if the specific manufacturing step being tested does not achieve its intended purpose, the manufacturing step may be revised and tested again, without subjecting actual device wafers to the unsatisfactory manufacturing step.
The industry, as a result of the extreme number and cost of the monitor wafers being used, currently attempts to recycle or reclaim these used monitor wafers. The recycling or reclaiming of the used monitor wafers typically begins by determining what type or characteristic of used monitor wafer is being recycled or reclaimed. Knowing that information, the specific type of chemical etch, chemical strip, and/or polish that is required to return the monitor wafer to a suitable state, may be determined.
Conventional technologies do not always thoroughly restore the original condition of a monitor wafer. For example, conventional technologies may not be capable of adequately removing or reducing the number of crystal oriented pits (COPs) or oxygen induced stacking faults (OISFs) that appear on the surface of the monitor wafers, thereby failing to make them sufficiently atomically flat. OISFs typically result when oxygen precipitates out of the wafers during one or more of the multiple thermal cycles the monitor wafers experience during testing. As the COPs and OISFs show up as light point defects, similar to airborne particles, the industry generally finds them undesirable. This becomes an even greater problem as industry monitor wafer specification requirements tighten. For example, whereas industry specifications previously required about 25 particles of 0.2 microns or less per wafer, in certain instances the industry now requires less than about 25 particles of 0.16 microns or less. With the current two-step or three-step polishing processes for recycled/reclaimed wafers, COPs and other crystal oriented front surface defects are still quite abundant at the sub 0.17 micron level. If the COPs or OISFs can be removed from this count, the manufacturers' defect specifications are easier to attain.
Therefore, what is needed in the art is a method for recycling/reclaiming silicon wafers that addresses the drawbacks of the prior art processes.